In the manufacture of temperature measuring devices, there is, for example, the long-used technology, wherein temperature sensors, especially platinum resistance sensors in thin film embodiment, are encapsulated, or embedded, in, given cases, pure ceramic powders (MgO,Al2O3).In such cases, most often a number of goals are pursued: on the one hand, the, in general, scarcely rugged sensor elements should be secured. On the other hand, the connection wires of the sensor elements should be electrically insulated relative to one another, and also from a metal housing, for example a thermometer jacket, for service at high temperatures of 600° C. or more. Furthermore, impurities and/or chemical changes of the sensor element ( especially temperature-sensitive, platinum, thin film sensors) should be excluded for as long a time as possible. The achievement of these goals is most often limited in practice.
Better results achieved when, instead of a more or less compressed ceramic powder, a ceramic casting which hardens by curing is used, and the sensor element is securely embedded and encapsulated in a compact, comparatively fixed, ceramic block. As a mold, into which the ceramic casting and the sensor element are inserted and cured, options include either small, fitted, ceramic parts (e.g. small tubes) or even a steel tip, or casing of the measuring device, or of the thermometer itself, into which the sensor element to is installed. In such a case, the volume of casting material to be charged is comparatively small, e.g. only a few 100 mm3.
Most often for such ceramic castings, greater amounts of fine powder is mixed separately with water or other liquid in a fixed mass ratio and then charged into the mold, where setting and hardening slowly occur. However, a batch of ceramic castings, after mixing, is, like plaster for example, capable of being cast and dispensed for only a relatively short time (a few minutes). Thereafter, solidification sets in, so that this casting material is scarcely still conveyable and can no longer be metered with established methods. This is the more so true, when small fill volumes are involved. A casting apparatus applied for this casting would be continually complex to clean, and a large part of the mixed ceramic casting material would be unusable.